TOKYO — Cooling systems were restored for four fuel storage pools at Japan's tsunami-damaged nuclear plant, more than a day after a power outage halted the supply of fresh cooling water and raised concerns about the safety of the facility, which still relies on makeshift equipment.

Tokyo Electric Power Co. said the cooling system at the last pool at the Fukushima Dai-ichi plant was repaired early Wednesday. It said pool temperatures were well within safe levels and the reactors were unaffected.

TEPCO spokesman Yoshikazu Nagai said workers were still trying to determine the cause of the cooling failure, which began when a brief power blackout hit the plant Tuesday evening.

About 50 workers in hazmat suits and full-face masks were mobilized to fix the cabling to three switchboards that were suspected of involvement in the problem. TEPCO also prepared a backup system in case the repairs didn't fix the issue and "worse comes to worst," company spokesman Masayuki Ono said earlier Tuesday.

A massive earthquake and tsunami on March 11, 2011, caused extensive damage to the plant. Massive radiation leaks at that time contaminated air, water and soil around the plant, causing some 160,000 residents to evacuate.

The latest power outage was a test for TEPCO to show if it has learned anything from the disaster. TEPCO, which has faced repeated cover-up scandals, was slammed by local media Tuesday for waiting hours to disclose the blackout.

Ono acknowledged the plant was vulnerable.

"Fukushima Dai-ichi still runs on makeshift equipment, and we are trying to switch to something more permanent and dependable, which is more desirable," he said. "Considering the equipment situation, we may be pushing a little too hard."

Ono said the utility did not immediately try to switch to a backup cooling system because doing so without finding and fixing the cause could lead to a repeat of the problem.

There is a backup cooling system but no backup outside power source. TEPCO has backup cooling systems with separate power sources for reactor cooling, but fuel storage pools only have emergency diesel generators as a backup. TEPCO said it will consider installing backup outside power for the pools.

The Unit 3 and 4 reactors share a makeshift switchboard that sits on the back of a truck, but an upgrade to a permanent, safer location is being planned later this month. Reactor cooling water pumps also sit on the back of a truck, with hoses traveling several kilometers (miles) to reach the reactors.

"We have a ton of problems that still need to be taken care of to overcome the challenges that we have never experienced before," Ono said. But he denied the power outage would affect the plant's long-term cleanup plans.

Regulators have raised concerns about the makeshift equipment and urged the plant to switch to a more permanent arrangement. The operator still has to remove melted, highly radioactive fuel from the reactors before fully decommissioning the plant, which officials say could take 40 years.

Chief government spokesman Yoshihide Suga sought to allay concerns.

"We have put in place measures that leave no room for worry," Suga told a regular briefing.

The command center at the plant suffered a brief power outage before 7 p.m. Monday. Electricity was quickly restored there but not to equipment pumping water into the fuel pools.

The temperature in the four pools had risen slightly, but was well below the utility's target control temperature of 65 degrees Celsius, TEPCO said.

"We don't believe the Fukushima disaster is under control," said Yuko Endo, chief of nearby Kawauchi village, part of which remains restricted because of radiation contamination, keeping hundreds of residents away from their homes. Officials are struggling to make the area livable again, but people cannot return home unless they feel confident about the plant's stability, he said.